A chain saw is commonly used to fell, buck and delimb trees. The saw chain, the power head and the coupling components that made up a wood cutting chain saw have been highly developed. The steel cutting links of the saw chain slide along a steel guide bar at a high rate of speed driven by a drive sprocket connected to the drive shaft of the power head. The guide bar is a plate-like member with an oval guide edge provided with a guide slot flanked by guide rails. The saw chain is made up of interconnected center and side link pairs. The center links include a depending tang that slides in the guide groove and the side links have bottom edges that slide on the guide rails.
The cutting links which are commonly provided as one of the side links of each pair of side links, have an upwardly or outwardly extended portion formed into forwardly directed cutting edges. These cutting edges engage the wood body and cut out wood chips.
The entire process of wood cutting with a chain saw involves metal sliding on metal and metal pounding on metal in reaction to the fast moving chain engaging the wood and removing chips. The wear problem is extremely acute and yet has been largely overcome by metal processing technologies that provide hard metal where wear resistance is desirable, ductile metal where fatigue resistance is desirable, etc. All of this enables the production of a commercially feasible wood cutting tool, i.e. a chain saw with a reasonable life expectancy at a reasonable cost.
Cutting concrete, stone and other hard, brittle materials requires a different type of cutting edge than that used to cut wood. Typically such materials are cut with small cutting blocks composed of a metal matrix having graded industrial diamond particles impregnated therein. The blocks are attached to a cutting tool, i.e. to the periphery of a circular blade, or to a steel cable. Most commonly used are the circular blades, and the chain saw of the present invention will be compared to the circular blade in demonstrating the benefits of the invention.
The circular blades are driven by a shaft through the blade center. The blade has to be quite large in comparison to the depth of cut desired. For example, the diameter of the blade needs to be about three times the required depth of cut. Thus, if a ten inch wall is to be cut, the blade has to be about thirty inches in diameter. The power head for driving such a blade has to be correspondingly powered and the power head and diamond carrier blade in combination make up a very costly cutting tool. A guide bar and chain for a chain saw designed for a comparable operation (thickness of material to be cut) is about 8% of the weight and volume of a circular saw blade. This is indicative of the benefits to be derived from a satisfactory concrete cutting chain saw.
The circular blade has a further problem in a fairly common concrete cutting situation. The exposed cutting face of the circular saw is the partial circumference of a circle, i.e. about a 120 degree segment of a circle. As long as the cutting area of the blade can be extended clear through the thickness of the material and then continued past both ends of the material being cut, the circular cutting face is not a problem. But consider for example a concrete wall that is 10 inches thick and extends between a ceiling and a floor. When the blade has been fully projected up and down the wall (but without being extended into the floor or ceiling) there remains a substantial uncut portion of the wall that may extend as much as 6 inches or so down from the ceiling and up from the floor. This remaining portion has to be cut by another tool and previously no such tool existed that was considered satisfactory for the task.
Chain saws have, of course, been considered. A patent as early as May 2, 1899, U.S. Pat. No. 624,400, disclosed the use of a cutting chain for cutting earth and rock. More recently aggregate cutting saw chain and chain saws were disclosed in U.S. Pat. No. 2,912,968 (Nov. 17, 1959), U.S. Pat. No. 3,545,422 (Dec. 8, 1970), U.S. Pat. No. 3,593,700 (July 20, 1971), and U.S. Pat. No. 4,181,115 (Jan. 1, 1980). To out knowledge, none have been successful.
There are several problems that are encountered by chain saws that do not exist for circular saws. The saw chain and guide system involve numerous parts sliding against each other. The side links and center links pivot relative to each other on rivets or pins; the side link bottom edges slide on the guide bar rails; and center link drive tangs slide in the guide bar groove. Whereas technology developed heretofore enables this sliding relationship for wood cutting, that is not the case for aggregate cutting.
When cutting cement and stone, fine particles are ground out of the aggregate medium creating a dust that settles on the saw chain and its components. This dust gets between the sliding parts of the bar and chain links and acts as an abrasive to rapidly wear the hardest of steel surfaces. Also the heat that is generated in cutting the hard aggregate materials is so high that similar steel to steel sliding creates an "adhesive" type of wear between engaging parts. This is an inherent welding action that takes place due to the extensive heat that is generated between the parts. Beads of the material are formed in this welding process that break off as particles. Over a period of time (a relatively short period of time where this process is continuous) the engaging surfaces are rapidly worn away.
The above problems are however, secondary. The primary problem is the provision of a cutting element with sufficient life. Obviously if the cutting element cannot be retained by the saw chain for any period of time, the fact that the moving or sliding parts are rapidly wearing is of little consequence. The cutting element that is desired for cutting through aggregate material is a metal matrix impregnated with diamonds. It is not practical to make the cutting links entirely of this material.
Most commonly the bar and saw chain links are made of steel as in wood cutting chain and a cutting block of the diamond impregnated matrix is bonded to the saw chain. Typically, the side links have upper body portions that are configured to support the cutting blocks and the cutting blocks are bonded to a saw chain link as by brazing. All such attempts have failed either because the bond wouldn't hold, the bonding process detrimentally effected the wear life of the chain, the chain became too costly, or a combination of all three.
Nothing prior to this invention has been successfully developed to secure a cutting block to the saw chain sufficiently to withstand the extreme abuse that is encountered in an aggregate cutting operation.